1. A quantity of material, such as cells, that unite or adhere to each other. 2. Soft solid preparation for internal use and of such consistency that it may be molded into pills. 3. A fundamental scalar property of an object that describes the amount of acceleration an object will have when a given force is applied to it. The metric unit of mass is the kilogram. One kilogram equals 2.205 pounds. SEE: weight4. Large, extensive, or encompassing an entire organ or population group, e.g., a mass vaccination.